1. Field of the Invention
This invention relates generally to fluid mixing assemblies, and more particularly to an assembly for suppressing noise of a jet engine.
2. Description of the Prior Art
With the advent of the jet engine, there was and is the concomitant problem of noise. Jet noise is produced by the turbulent fluctuations in the jet formed from the hot core and bypass flows. It is responsible for the lower frequency components of engine noise which are difficult to reduce using standard acoustical techniques. Jet noise reduction has been achieved by mixing the jet exhaust flow with the ambient air at the expense of large thrust losses, reduced payload and range due to increased aircraft weight, and increased mechanical complexity.
Since jet noise is a sensitive function of the jet velocity, V, with the noise power varying as V.sup.8 for subsonic flows and V.sup.3 for supersonic flows, jet velocity reduction is a prime approach. The objective of most techniques is to reduce the jet velocity by increasing the mixing between the jet and ambient flows.
For currently flying commercial aircraft moderate reductions in noise level are desired, but would be implemented only if the cost to flight performance was very small. For the proposed supersonic aircraft the required noise reduction is large, but somewhat larger penalties are permissible. However, the state of the art in either subsonic or supersonic applications does not justify the use of current technology to reduce jet noise because of performance penalties and hardware complexity.
The use of small auxiliary jet flows to interact with the main jet flow to increase mixing could reduce the amount of hardware needed and thus reduce the flight performance penalties. It has been shown that the interaction of two small radial jets with a subsonic main jet did increase mixing, but noise measurements were not taken. Reductions in so-called "screech" noise for supersonic jets was formed when small jets intersected a main jet at a shallow angle.
Prior art attempts at jet noise reduction were also directed to the modification of the exhaust nozzle systems manifested through the deformation of exhaust nozzle cross-section into a series of lobes, chutes or individual tubes.
While somewhat effective, there remains the need for an assembly to further reduce jet engine noises, particularly during take-off of the aircraft.